The invention relates to improvements in apparatus for convoluting a stream of sheets on a core, especially for convoluting a scalloped stream of partially overlapping paper sheets which are provided with printed matter. More particularly, the invention relates to improvements in apparatus of the type disclosed in commonly owned U.S. Pat. No. 4,523,751 granted June 18, 1985 to Peter Merkli for "Apparatus for convoluting sheets of paper on a core".
Apparatus of the type to which the present invention pertains are further disclosed in published European patent application No. 135 080 and in published German patent applications Nos. 32 21 153 and 32 31 427. Such apparatus employ a single narrow elastic band, one end portion of which is attached to a first core serving to store a series of sheets and the other end portion of which is affixed to a second core serving for temporary storage of unused portion of the band. A drawback of these conventional apparatus is that the relatively narrow band is not always capable of adequately holding the convolutions of paper sheets on the first core, especially if the sheets are folded and are gathered into a series of partially overlapping stacks, such as signatures or inserts for newspapers. Folding of sheets results in formations which are thicker along the fold lines, and this creates problems when a single narrow band is used to form convolutions which alternate with the convolutions of a stream of partially overlapping folded sheets in order to form a large roll of the type used for temporary storage of insets for weekend editions of newspapers. One of the present known solutions includes reducing the dimensions of the roll so as to ensure that a single narrow band will be capable of properly retaining such sheets. In accordance with another known proposal (disclosed in published German patent application No. 25 44 135), the apparatus is equipped with three cores, namely a first core for collection of a large roll of convoluted paper sheets, a second core for a first elastic band, and a second core for a second elastic band. The two bands are convoluted onto two axially spaced-apart portions of the first core to thus ensure reliable retention of convoluted sheets in optimum positions for temporary storage on the first core. A drawback of such proposal is that the utilization of two elastic bands which are convoluted on discrete cores contributes significantly to space requirements and cost of the apparatus. Thus, it is necessary to provide an additional core as well as room for the additional core, and it is further necessary to provide a discrete drive and a discrete brake for the additional core as well as numerous pulleys for the second band.